The invention relates in general to devices involving ohmic contacts to n-doped InP layers. In particular, it is directed to devices comprising low-resistive, Au-free ohmic contacts obtained by annealing a stack of alternating layers of silicon and nickel. Such contacts can notably be used to inject current into components based on III-V semiconductors. Embodiments of the present invention can therefore find applications in the field of optical amplifier devices and silicon photonic circuit devices.
Silicon photonics relate to photonic systems, where silicon is used as medium for light propagation because of the material's low optical loss. Silicon photonics makes use of well-established silicon manufacturing principles exploited in complementary metal-oxide semiconductor (CMOS) electronics. The features are usually patterned into micro-photonic components with sub-micron precision (to operate in the infrared). Silicon on insulator (SOI) is typically used as a material of choice. The fabrication of silicon photonic devices can otherwise involve known semiconductor fabrication techniques; since silicon is already used as a substrate of choice for most integrated circuits, it is possible to create hybrid devices in which the optical and electronic components are integrated onto a single chip.
Integrated optical interconnects with compatible light sources are needed for mass-fabrication of low-cost, high-performance CMOS-based chips. Due to the indirect band gap of silicon, no Si-based light source is available. Efficient light sources are typically based on III-V semiconductors which are heterogeneously or hybrid integrated on a Si photonics platform.
The successful monolithic integration of components such as III-V semiconductor lasers on silicon requires shallow components, e.g., III-V gain stacks of less than 500 nm. Furthermore, the contact layers for injecting current need be moderately doped. This is necessary to achieve low absorption losses and thereby preserve the actual lasing action. On the other hand, moderately doped contact layers do usually not allow for low specific contact resistivities, i.e., specific contact resistivities of less than 10−6 Ω·cm2. A low contact resistance, however, is desired to reduce power dissipation. This is for instance needed to reduce thermal dissipation of an integrated laser and, in turn, increase its efficiency, by consuming less energy and having less thermal footprint.